Various surface coatings have heretofore been carried out for the purpose of improving characteristics of surface smoothness, abrasion resistance, corrosion resistance, surface hardness and the like, or for the purpose of an appearance decoration.
The surface coating methods include a vacuum evaporation method, sputtering method and the like. However, such methods are disadvantageous in that the equipment is expensive, it is difficult to form a thick coating layer, and so on.
Another method is a screen printing method wherein a paste comprising an inorganic powder and a resin binder as main components is coated and burned. However, the screen printing method has many disadvantages such as the thickness of film formed at a time is limited, the operability is poor, printing on a curved surface is very difficult, and the like.
On the other hand, a glazed ceramic substrate is a ceramic substrate thinly coated with a uniformly molten glass, and is used for a hybrid IC, a thermal printer head, etc. A thin film circuit is formed by forming a thin film on the glazed ceramic substrate by the vacuum evaporation method, sputtering method, etc. and patterning by photolithography. Accordingly, the smoothness of the surface becomes particularly important to improve a pattern accuracy of the circuit.
For the coating of glass on ceramic substrate, it has hitherto been most popular to coat a paste comprising a glass powder and a vehicle by means of the screen printing method.
However, this method has disadvantages that mutiple printings must be carried out because it is difficult to form the necessary coating thickness at a time, the operability is poor, and the accuracy of the coating thickness is poor. A further disadvantage is that surface defects occur because of bubbles entrapped at the time of printing.
In view of the above situation, a method for press-bonding a green sheet comprising a glass powder and a binder as main components to a ceramic substrate was proposed as a method for easily producing a glazed ceramic substrate having excellent thickness accuracy as disclosed in JP-A-61-22682 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). However, it has a problem that the bonding strength between the green sheet and the ceramic substrate is weak. In order to improve the bonding strength, increasing the amount of the binder added or lowering Tg (glass transition temperature) of the binder was considered. However, problems still arise in that the former tends to form pinholes at burning due to the lowering of the packing density of glass powder and the latter lowers strength of the green sheet, making the sheet difficult to handle. Further, since the green sheet is press-bonded to the ceramic substrate with the binder, another disadvantage is that when the temperature is raised in the subsequent burning step, the bonding strength decreases before the binder disappears, and an edge shrinkage of the glazing part occurs.
To track parts in any production system it is useful to have an identification label having production data on it such as necessary resistances, heat-resistance, resistance to chemicals, etc. This helps to control products, semi-fabricated products, parts, etc. Resistances are particularly necessary for the identification label to control glass products, metal products, sintered ceramic products, etc.
Heretofore, as an identification label which directly sticks to an article to be adhered and has a durability, heat resistance, resistance to chemicals, etc., labels comprising a substrate such as sintered ceramic, stainless steel, enameled ware, etc. have been known. However, such identification labels have involved various disadvantages in that they had to be screwed on, which takes time, they were too inflexible to be affixed to curved surfaces easily, and it was difficult to form a pattern with excellent heat resistance at a job site.